Preparation of guanidine salts



Patented Oct. 3, 1950 PREPARATION OF GUANIDINE SALTS William H. Hill,Pittsburgh, Pa., assignor to Koppers Company, Inc., Pittsburgh, Pa., acorporation of Delaware No Drawing. Application June 17, 1947, SerialNo. 755,237

8 Claims.

The present invention relates to an improved process for the preparationof guanidine and guanidine salts from ammonium thiocyanate. The presentapplication is a continuation in part of inventors application, SerialNo. 548,635, filed Aug. 8, 1944, now abandoned.

When ammonium thiocyanate is fused and heated at a temperature of about180 0., the mass is converted by prolonged heating to guanidinethiocyanate and hydrogen sulfide is evolved. The reaction, which is wellknown, proceeds according to the equation:

This equation illustrates the fact that two mols of ammonium thiocyanateare required to produce one mol of the guanidine salt and, therefore,upon the basis of the mol weight of ammonium thiocyanate employedatheoretical yield of 50% by mol weight of guanidine compound can beobtained. It was further recognized in the prior art that the reactionshown above does not proceed quantitatively either because some of thehydrogen sulfide remains in the melt and. inhibits the progress of thereaction to the right or because undesirable side reactions occurbetween hydrogen sulfide and further quantities of ammonium thiocyanatecausing decomposition of the latter with evolution of carbon disulfide.Wilhelm Gluud, in U. S. 1,902,400, obtained a substantial increase inthe yields from the process by introducing gaseous ammonia into thereaction mass and therewith sweeping hydrogen sulfide from the melt. TheGluud process provided improvement over the former expedient ofemploying heavy metals to react with the hydrogen sulfide, as is pointedout in the aforesaid patent, but, of course, the problem of theevolution of hydrogen sulfide, a highly noxious gas, ,4

still remained and furthermore two mols of ammonium thiocyanate werestill required to produce one mol of guanidine salt.

An object of the present invention is to provide a novel process forpromoting the conver-' sion of ammonium thiocyanate to guanidine byfusion of ammonium thiocyanate at an elevated temperature.

Another object of the invention is to provide a novel process forobtaining said conversion without the disadvantageous evolution ofhydrogen sulfide experienced in the prior art.

A further object of invention is to provide a novel process wherebyenhanced yields of guanidine can be obtained in a single fusion step'in2 relatively short reaction times from ammonium thiocyanate. r

The invention has for further objects such other improvements and suchother operative advantages or results as may be found to obtain in theprocesses or apparatus hereinafter described or claimed.

According to the-present invention, ammonium thiocyanate, or its isomer,thiourea, is fused with a sulfuric acid derivative such as sulfamide,S111- fimide, and alkali or alkaline earth metal salts of sulfamic acidor imido-disulfonic acid. The selected compound reacts with the ammoniumthiocyanate in molten admixture therewith, and oxidizes the sulfur ofthe thiocyanate-radical to elemental sulfur which separates out of themelt. The product of the reaction isa guanidine salt or a mixture ofguanidine salts which can be readily converted to free guanidine orknown guanidinesalts.

The said sulfuric acid derivatives constitute the class of compoundsproduced by successive replacement of hydroxyl groups in sulfuric acidby the. amino." group as defined in Degering An Outline of ,OrganicNitrogen Compounds, page 477, paragraph M29. The initial compound of theseries is sulfamic acid H2N.SO2OH, which series in addition includesimidodisulfom'c acid, and sulfamide and sulfimide.

, In the claims the term alkali metal is intended to include the NH4group.

Either ammonium thiocyanate or thiourea can be employed as the startingmaterial in the reaction. Thiourea is produced by heating am-.

monium thiocyanate and this conversion probably occurs initially whenthe present reaction is carried out. The employment in the fusion meltof one of the above compounds with ammonium thiocyanate providesremarkably enhanced yields probably because in the reaction melt theamino groups of the aforementioned sulfuric acid derivatives supplyammonia to the formation of the guanidine and consequently from one molof ammonium thiocyanate a theoretical yield constituting one mol ofguanidine salts can be obtained. Furthermore, the hydrogen sulfide,previously evolved when ammonium thiocyanate is heated, is in this newprocess by the action of the said sulfuric acid derivatives oxidized toelemental sulfur which is insoluble in the melt. Consequently, thedisadvantageous evolution of hydrogen sulfide, and the undesirableinhibition of the progress of the reaction to completion that wasformerly caused by the presence of dissolved hydrogen sulfide, areeliminated.

For example, such compounds as sulfamide (SO2(NH2) 2) alkali sulfamatessuch as ammonium sulfamate (NliiOsOzNHzl, sodium sulfamate (NaOSOzNHz),and. potassium sulfamate (KOSO2NH2) and ammonium imidodisulfonate(HN(SO2ONH4) 2) have been found of special utility for providingimproved yields of guanidine according to the present improvement.

In the conversion reaction products, the guanidine is found incombination with sulfur-oxygen acid radicals, thus making available forconversion to guanidine that thiocyanate radical which heretofore hasalways been found in combination with the guanidine when ammoniumthiocyanate is heated alone.

Advantageously the conversion reaction of amvvmonium thiocyanate withderivatives of the aforementioned type proceeds with substantially noevolution of th usual hydrogen sulfide from the reaction mixture andfurthermore there is exhibited by their use a surprising increase in thevelocity of formation of guanidine and, thus in a given reaction time,animportant increase in yield of guanidine is recoverable from a givenquantity of the employed thiocyanate. As a byproduct, instead ofhydrogen sulfide, elemental sulfur appears in th reaction product.

The ratio of reactants practicably employa'ble ,in the present inventioncan be varied considerably, and can be used to effect corresponding 1variations in reaction phenomena and yield. In. general, it can be saidthat it is preferred to use about equimolar ratios of ammoniumthiocyanate and an aforesaid compound; in the case of ammoniumsulfamate, in particular, it has been found that more than one mole ofammonium sulfamate makes possible the reduction of the reactiontemperature or the reaction time that -is required to produce a givendegree of conversion of ammonium thiocyanate in a single heating step.By the use of ammonium sulfamate,

homogeneous melts can be produced at low temperature so that before asubstantial conversion ofammonium thiocyanate is initiated, the reactionmixture is substantially homogeneous in composition. When the molarratio of ammonium sulfamate to ammonium thiocyanate in the admixture isabout 2:1 a homogeneous melt is obtained at a temperature as low as 80C. At the preferred temperature of reaction, 190 C., if a mixture ofammonium sulfamate and ammonium thiocyanate is heated for eleven hours,and the molar proportion of ammonium sulfamate to ammonium thiocyanateis 1% 1 instead of in molar equivalency, the yield of recoverableguanidine is substantially fifteen percent greater than with a molarratio of 1:1, and the decrease of residual ammonium thiocyanate in theresultant mixture is substantially thirty percent.

reaction begins to convert to triazines and it is thus desirable whenguanidine is the only preferred product, to maintain the reaction meltat below about 200 C. The higher temperatures can give rise to excessivedecomposition of sulfamate which is unproductive of guanidine.

Other things being equal, the rate at which equilibrium is attained inthe reaction mixture depends, to a pronounced degree, on the temperatureof reaction. For example, equal quantities of a given admixture ofammonium thiocyanate and ammonium sulfamate were separately heated at aconversion temperature; the one to C. for eleven hours, and the other toC. for one hour and a half. The conversions of ammonium thiocyanate inboth instances were substantially equal. Continued heating of the lattermixture at 190 C. for eleven hours gave a yield of approximatelninety-five percent of guanidine based on the Weight of ammoniumthiocyanate employed One of the advantages of the present improvementresides in the fact that homogeneous, fused mixtures of ammoniumthiocyante and an aforesaid reactant can be provided at temperatures aslow as 80 C. thereby avoiding the obvious disadvantages of reactingmixed reactants that are in heterogeneous admixture. For any specificapplication, therefore, of the present improvement, the employedtemperature of heating resides within the skill of the art and candepend upon the preferred rate of conversion, degree of conversion, andthe temperature attainable in existing equipment after fusion isattained.

As aforementioned, the guanidine content of the reaction productsobtained is combined with acid in the form of a salt or salts. Theprecise constitution of the acid radicals is not known, but it has beendetermined that they are acids of oxides of sulfur. It is believed thatthe reaction product, when ammonium sulfamate is employed, is guanidinesulfinate, and that, in other instances, similar reducedsulfur-oxygen-amine radicals form the acid radical. However, inasmuch asthese acid radicals are unstable or are readily convertible to knownsalts such as sulfates, and as the guanidine radical is obviously theone of importance in guanidine production, the process is not limited toa delineation of any particular acid radical.

The product of reaction is useful directly as a concentrated fertilizer;it is especiall valuable where a slower delivery of nitrogen to the soilis desired than that delivery provided by ammonium salts or urea. Theelemental sulfur in the said reaction-product is particularly useful inthe treatment and fertilizing of alkali soils and in the control offungi and soil-borne diseases. The sulfur can be maintained by agitatingmeans in uniform dispersion throughout the melt during its cooling downto temperature of solidification. The aqueous extract is useful also bvirtue of its guanidine content as an ingredient in fireproofing agentsand as an intermediate in the preparation of dyestuffs, explosives,leather chemicals and pharmaceuticals.

Guanidine in salt form is readily obtainable from the reaction-productsof ammonium thiccyanate and the aforementioned reactants by leachingthem with water thereby forming aqueous solutions of guanidine saltsthat als contain soluble ammonium or other alkali salts. When theleaching is carried out with warm Water, the so-formed solution containsguanidine sulfate and. bisulfate, (the guanidine sulfinate apparentlydecomposing in the same manner as ammonium sulfinate or amidosulfite inwhich case much sulphate is formed. Cf. Divers and Ogawa J. C. 8., vol.77, p. 327 or p. 335) and, in addition, some ammonium or other alkalisulfate, depending up n the above reactant employed. The solution isthen treated with limited quantities of alkalineearth metal oxide orhydroxide under conditions to remove substantially only all the free orcombined ammonia from the leached solution and to precipitate onlyalkaline-earth metal sulfates and sulfites if present. So-treatedsolution contains after filtration or centrifugalization substantiallyonly guanidine sulfate, which can by customary methods, such asevaporation, or the like, be readily recovered therefrom.

In the preparation of other guanidine salts from the said guanidinesulfate solution by double decomposition, preferably a sodium salt ofthe desired anion to be combined with the guanidine is employed so as totake advantage, in the recovery of the said other salt by fractionalcrystallization, of the decreasing solubility of sodium sulfate withincrease in temperature.

Free guanidine can be liberated from the said guanidine sulfate solutionby treating the same with a base of greater alkalinity than guanidine,

such as an alkali metal hydroxide.

The following equation is given to illustrate the summation of thereactions believed to occur when ammonium thiocyanate and ammoniumsulfama'te are reacted according to the invention, and to serve asa-basis for calculating the yields obtained in the following specificex- The guanidine amido sulfinate which is assumed to be the reactionproduct in the above empirical equation is apparently unstable; in anyevent, upon leaching, the reaction product is guanidine sulfate, theoxidation of the unstable sulfite compound apparently being effected bythe presence of air during leaching as is noted for example in Ephraim,Inorganic Chemistry 4th Ed., p. 563 or in the aforesaid J. C. S.reference.

In the above discussion of the present improvement, reference has beenmade only to ammonium thiocyanate as the source of guanidine. Thedescribed processes are, however, applicable to thiourea as the startingmaterial and also to mixtures of thiourea and ammonium thiocyanate ofwhich both give substantially the same yields of guanidine.

The following examples serve to illustrate the present invention but inno instance are intended to limit the same.

EXAMPLE 1 In each of six test tubes-a sample of a mix containing byweight 98 parts of NI-I4SO3NH. and 52 parts of NI-I4SCN (a mola'r ratioof, respectively, 1 11) was heated in an oil bath maintained at 190 C.During the'period of reaction the contents of'each were stirred. After areaction period of 1, 3, 5, 7, 9 and 11 hours, a test tube was removedfrom the bath, andthe loss of material by vaporization of volatileproducts was determined. There was no evolution of H28 thus indicatingthat an oxidation of the sulfur had occurred. 1

The products in each case were leached with water and the undissolvedportion was considered as sulfur, although'a small amount of triazinesmight have been included therewith. The dissolved material was analyzedfor guanidine. The Table 1 hereinbelow recorded gives the content of thestated products of the six samples.

From inspection of the above table it can be seen that 94% oftheoretical yield of guanidine was obtained after retention of theammonium thiocyanate and ammonium sulfamate melt at 190 C. for elevenhours.

EXAMPLE 2 76 parts of NHSCN and 228 parts of NH4SO3NH2 by weight wereheated and reacted in an open vessel. A thin, clear, bluish melt wasobtained at about C., the color being due to elemental sulfurcolloidally dispersed in the melt; at about C. the melt became colorlessand contained a cloudy suspension. At

about C. yellow sulfur appeared, and at about 210 C. the rate ofreaction and of temperature rise became accelerated and the temperaturerose abruptly to 245 C. Total reaction time was about 10 minutes. Therewas no evolution of hydrogen sulfide.

Analysis of the aqueous solution produced by leaching showed that 44parts of guanidine had been formed, or 75% of theoretical yield, basedon the weight of NIIQSCN employed. About 17% of the original ammoniumthiocyanate remained unreacted in the solution.

EXAMPLE 3 By weight, 60 parts of thiourea and 90 parts of ammoniumsulfamate (molar ratio of 1:1) were heated and reacted together for fivehours in a glass vessel immersed in an oil bath maintained at C. Noevolution of hydrogen sulfide was observed. The reaction product wasthen cooled and leached with water leaving elemental sulfur as residue.The aqueous solution 'so obtained was analyzed for its guanidine contentwhich was 69.2% of theoretical yield based on the weight of thioureaemployed. The elemental sulfur residue was 17.1% by weight of .theemployed admixture.

EXAMPLE 4 By weight, 58.5 parts of ammonium thiocyanate and 91.5 partsof sodium sulfamate (molar ratio of 1:1) were heated and reactedtogether according to the procedure described in Example 3. No evolutionof hydrogen sulfide was observed. The aqueous solution obtained byleaching the reaction product with water showed that 61.8% oftheoreticalyield of guanidine based on the employed weight of ammoniumthiocyanate was obtained. The elemental sulfur residue was 14.8% byweight of the employed admixture.

EXAMPLE 5 By weight, 22.1 parts of ammonium thiocyanate and 61.3 partsof ammonium imidodisulfonate (molar ratio of 1:1) were heated andreacted together according to the procedure described in Example 3. Noevolution of hydrogen sulfide was observed. The aqueous solutionobtained by leaching contained 73.1% of theoretical yield of guanidinebased on the weight of ammonium thiocyanate employed. The elementalsulfur resi due was 11.7% by weight of the employed admixture.

EXAIVIPLE 6 By weight, 47.5 parts of ammonium thiocyanate and 60 partsof sulfamide (molar ratio of 1:1) were heated together according to theprocedure described in Example 3. No evolution of hydro-,

gen sulfide was observed. 70.4% of theoretical yield of guanidine basedon the employed weight of ammonium thiocyanate was obtained. Theelemental sulfur residue was 19.8% by weight of the employed admixture.

EXAMPLE 7 By weight, 60 parts of ammonium thiocyanate and 90 parts ofammonium sulfamate (molar ratio of 1:1) were heated together accordingto the procedure described in Example 3. No evolution of hydrogensulfide was observed. The aqueous solution obtained by leaching thereaction product with water showed that 64.1% of theoretical yield ofguanidine based on the employed Weight of ammonium thiocyanate wasobtained. The elemental sulfur residue was 15.5% by weight of theemployed admixture.

EXAMPLE8 By weight, 51 parts of ammonium thiocyanate and 99 parts ofcrude ammonium sulfamate, containing about 80% ammonium sulfamate andammonium sulfate (net molar ratio of the first two compounds was 1:1)were heated and reacted together according to the procedure described inExample 3. No evolution of hydrogen sulfide was observed. 64.8% oftheoretical yield of guanidine based on the employed weight of ammoniumthiocyanate was obtained. The elemental sulfur residue was 13.7% byweight of the employed admixture.

EXAMPLE 9 A mixture of 114 parts and 223 parts by weight, respectively,of ammonium thiocyanate and the crude ammonium sulfamate described inExample 8 were heated to 110 C. forming thereby a thin melt. Theammonium sulfate was removed by filtering in a hot funnel and thefiltrate was cooled. 150 grams of the cooled filtrate, having a molarratio of 1:1 of thiocyanate to net sulfamate, were reacted according tothe procedure described in Example 3. No evolution of hydrogen sulfidewas observed. 60.2% of theoretical yield of guanidine based on theemployed weight of ammonium thiocyanate was obtained. The elementalsulfur was 14.7% by weight of the employed cooled filtrate.

EXAMPLE 10 As a further example in the preparation of guanidine compoundaccording to the present invention, a series of tests was run in eachinstance of which 114 grams of ammonium sulfamate were heated inmoltenadmixture with 76 grams of ammonium thiocyanate at varying temperaturesand for periods of one, three and five hours. The melts were reacted forthe three time periods at temperatures of 180 0., 200 0., and 210 C. Inno instance was any evolution of hydrogen sulfide detected. In all casesproduced insoluble solids were separated from a filtrate consisting ofan aqueous solution of the obtained guanidine salt. The solids wereanalyzed for sulfur and nitrogen, which is hereinafter reported also aspercent triazines calculated as melamine inasmuch as it is the leadingmember of the series of triazines adventitiously produced by thereaction.

Analyses of Insolublcs In 1 sYifild, so uu ur, 1 83 bles. Wt. Nitro-Triazines Sulfur, Per Cent in Gms gen, Per (Cale) Per Cent of Gent byPer Cent by Theory Weight by Weight Weight 1. 180 4. 9 0. 054 0. 08 94.81 14. 5 3 180 11. 2 0. 0. 16 94. 40 33. O 5- 19. 0 0. O. 29 98. 45 58.4 1 200 20. 8 0. 238 O. 36 97. 45 63. 3 3- 200 23. 9 0. 808 1. 21 96. 6775. 2 5- 200 26. 4 1. 45 2.18 96. 64 79. 7 l- 210 25. O 2. l4 3. 21 93.93 73. 3 3 210 27. 3 4. 30 6. 45 93. 15 79. 5 5- 210 28. 6 4. 85 7. 2991. 33 81. 5

It is noted from the above table that the pro duction of elementalsulfur provides an index of the progress of the reaction. It is furtherobserved that after five hours of reaction at a temperature of210, ayield of 81.5% of the theoretical weight of sulfur is obtained. Inaddition to demonstrating the progress of the reaction at dif ferenttemperatures over different time periods the performed analyses provethat the solid which is produced is elemental sulfur. The presence ofelemental sulfur, in turn, necessarily demands the reduction of anotherreactant in order to provide for the oxidation of thiocyanate sulfur toelemental sulfur and therefore supports the assumption that the sulfuricacid derivative employed is reduced to a sulfur-oxygen compound of alower stage of oxidation.

It is noted that in the above specific examples the guanidine obtainedcould not possibly have resulted from a thermal decomposition ofammonium thiocyanate alone, because in every instance the yield ofguandine is over 50% and is, therefore, higher than the maximum yieldobtainable from heating ammonium thiocyanate alone.

In the claims, the starting material of the reaction is ammoniumthiocyanate. As is well known in the art, when ammonium thiocyanate isheated, thiourea, an isomer of thiocyanate is initially formed.Therefore, it is understood that in carrying out the process of thepresent invention the reacting of thiourea, which can find its sourceelsewhere than in ammonium thiocyanate, is an obvious equivalent to thereacting of ammonium thiocyanate as expressly set forth in the claims.

Many additional products of the reaction of the present invention can beproduced by changing the conditions employed, especially thetemperature. Such compounds producible by increasing the temperature ofreaction can be biguanid, melamine, melam, melem, melon, ammeline,ammelide, thioammeline, and thioammelide.

The invention as hereinabove set forth is embodied in particular formand manner but may be variously embodied within the scope of the claimshereinafter made.

I claim:

1. An improved process of converting ammonium thiocyanate toguanidine-containing salt comprising: heating a mixture consistingessentially of ammonium thiocyanate at a temperature between 80 and 245C. while in contact with a compound selected from the group consistingof alkali metal sulfamates, alkali metal imido-disulfonates, andsulfamide.

2. In a process of converting ammonium thiocyanate toguanidine-containing salt, heating a mixture consisting essentially ofammonium thiocyanate with sufiicient ammonium sulfamate as substantiallyto liquefy their admixture at a temperature of about 80 C., andcontinuing the heating within the temperature range of about 150 to 200C. and thereby eifecting reaction therebetween and forming guanidinesalt of a sulfur-oxygen acid in the liquefied admixture.

3. An improved process of converting ammonium thiocyanate toguanidine-containing salt comprising heating and reacting a mixtureconsisting essentially of ammonium thiocyanate and ammonium sulfamatewithin the temperature range of 150 to 200 C. to form a reaction productcomprising guanidine salt of a sulfur-oxygen acid.

4. A process of converting ammonium thiocyanate to a guanidine sulfatecomprising: heating and reacting ammonium thiocyanate at a temperaturebetween 80 and 245 C. with a compound selected from the group consistingof alkali metal sulfamates, alkali metal imido-disulfonates andsulfamide, treating the resulting reaction product with warm water andforming an aqueous solution of guanidine sulfates in contact withinsoluble residue, separating so-formed aqueous solution from insolubleresidue, adding to the so-separated aqueous solution an inorganic alkalibase in quantity to form a mildly a1- kaline solution to convert anyguanidine bisulfate present to the sulfate, driving off the free orcombined ammonia from the so-treated solution while precipitating asalkali salts the sulfates formerly present in forms other than guanidinesulfate, and separating the so-formed precipitate from the aqueoussolution of guanidine sulfate.

5. A process as claimed in claim 1 and wherein the said reactants are inthe molecular ratio of substantially 1:1.

6. A process as defined in claim 1 wherein the selected compound issulfamide.

7. The process defined in claim 1 in which the selected compound is analkali metal sulfamate.

8. The process defined in claim 1 in which ammonium thiocyanate and theselected compound are reacted in the molar ratio of substantially oneand one-quarter to one.

WILLIAM H. HILL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,262,935 Hill et al Nov. 18,1941 2,265,942 Hill Dec. 9, 1941 2,334,151 Thurston Nov. 9, 1943

1. AN IMPROVED PROCESS OF CONVERTING AMMONIUM THIOCYANATE TOGUANIDINE-CONTAINING SALT COMPRISING: HEATING A MIXTURE CONSISTINGESSENTIALLY OF AMMONIUM THIOCYANATE AT A TEMPERATURE BETWEEN 80* AND245*C. WHILE IN CONTACT WITH A COMPOUND SELECTED FROM THE GROUPCONSISTING OF ALKALI METAL SULFAMATES, ALKALI METAL IMIDO-DISULFONATES,AND SULFAMIDE.